Heat exchanger



jam 9 1951 H. o. MCMAHQN AL 2,37 2? HEAT EXCHANGER Filed Dc. 22, 1947 eSheets-Sheet 2 H. o. MCMAHON Er AL 76 Jan. 9, 1951 HEAT EXCHANGER Y eSheets-Sheet 6 Filed Dec. 22, 1947 fiajard 41mm;

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Patented Jan. 9, 1951 HEAT EXCHANGER Howard 0. McMahon, Lexington,Gustave A. Bleyle, Jr., Melrose, and Richard B. Hinckley, Dorchester,Mass., aasignors to Arthur D. Little, Inc., Cambridge, Mass., acorporation of Massachusetts Application December 22, 1947, Serial No.793,186

This inventionrelates to an improvement in heat exchangers and themethod of effecting an eflicient 'heat exchange between two or morefluids.

Numerous attempts have been made to produce heat exchangers whichare'ei'ficient and reliable in operation and relatively inexpensive tomanufacture, particularly in the application of heat transfer from onegaseous fluid to another, where the heat transfer rate is low andconsequently very large surface is required. To this end, heatexchangers embodying various types of laminated constructions have beensuggested. The majority of such suggestions have shown various forms ofextended surface brazed or soldered between sheets of metal andgenerally the laminated sheets extend in a direction parallel to thedirection of flow. Constructions such as are shown in Wilke, No.1,863,586 and Schubart, No. 1,734,274, employ laminations perpendicularto the direction of flow of thefluid streams and, although possessingcertain advantages, are nevertheless subject to serious objections whichlimit their utility.

In constructions exemplified in the former patent, which embodiesperforated metal plates interposed between gaskets of substantially theidentical size and shape, the interior walls of the fluid passages arecontinuous and the number of square feet of heat transfer surface isobjectionably low. The heat transfer coeflicient is also low so that theefficiency of the heat exchanger is poor. On the other hand, inconstructions exemplified in the latter patent, having screens or wire,mesh interposed between the gaskets defining several passageways, theheat transfer coeflicient and exposed surfaces are both quite high, butthe pressure drop is objectionably high.

Moreover, in such constructions the wire mesh not only actsinefliciently as a heat transfer medium, due to the fact that only halfthe metal (i. e., the strands running in one direction) is usedadvantageously, but also presents, due to its reticular structure, thedifficult problem of providing a fluid-tight seal about each of thepassages, particularly at high pressures. Hence,

sembIy problems, and also the difficulty of repro- 12 Claims. (o1,257-245) 'flcientand reliable exchanger designed so that itmay beadvantageously employed not only in various systems for separating fluidmixtures, but also in gas turbine and the like installations; to providea heat exchanger particularly suitable for use in reversible flowsystems which require 4 identical flow characteristics in each channelor passage and in'either direction; to provide a heat exchanger whichhas a great flexibility of design and construction so that, if desired,the size and length of the fluid passages and the various factorsaffecting flow characteristics, heat exchange, etc., can be varied ormodified to suit any particular requirement; to provide a heat exchangerwhich can be disassembled for cleaning and repair and readily assembledwithout the necessity of brazing, welding or soldering parts; and toprovide a heat exchanger which can be economicallymanufactured by massproduction methods with the assurance that each unit has substantial yidentical performance characteristics permittinglthe substitution orreplacement of one unit by another in any system without makingcompensating adjustments.

A more specific object'is to provide an improved method of andapparatusfor separating the components of a gaseous mixture, wherein the incomingmixture is subjected to a greater cooling action by the efliuent thanhas'heretofore been possible, thereby increasing the over-all efliciencyof the system.

Further objects relate to various features of construction and will beapparent from the consideration of the following description and theaccompanying drawings, wherein:

Fig. 1 is a schematic view of a part of a system for producing oxygenfrom compressed air, which I embodies a heat exchanger constructed inaccordance with the present invention;

Fig. 2 is an isometric exploded view illustrating the various parts ofthe heat exchanger shown n Fi 1;

Fig. 3 is an enlarged isometric view of one of the foraminous plates ofthe heat exchanger;

Fig. 4 is a section on the line 4-4 of Fig. 3;

Fig. 5 is an enlarged isometric view of one of the fenestrate separatorsof the heat exchanger;

Fig. 5a is a fragmentary vertical. section through an assemblage offoraminous plates formed on one face with integral separators of fullthickness;

Fig. 5b is a view similar to Fig. but showing foraminous plates formedon both faces with integral separators of half thickness;

Fig. 5c is a view similar to Fig. 5a, but showing a foraminous plateformed on both faces with an integral separator of full thickness, theplate alternating with plates having pierced openings;

Fig. 6 is an enlarged section through a group of the assembled plates ofthe heat exchanger, illustrating the flow characteristics through andabout the openings in the plates;

Fig. 6a is a view similar to Fig. 6 but showing foraminous plates formedwith tapered openings;

Fig. 7 is a perspective view illustrating a modified form of heatexchanger;

Fig. 8 is a longitudinal section through the header approximately on theline 8-8 of Fig. '7;

Figs. 9 and 10 are transverse sections through the header on the lines99 and Ill-l0, respectively, of Fig. 8;

llg. 11 is a top plan view of one of the foraminous plates;

Fig. 12 is an enlarged plan view of one of the fenestrate separators;

Fig. 13 is an enlarged detail of the foraminous plate and associatedseparator shown in Figs. 11

- and 12;

Fig. 14 is an enlarged section through the plate and associatedseparator shown in Fig. 13;

Fig. 15 is an isometric view of another form of heat exchanger;

Fig. 16 is an enlarged isometric view of the injector embodied in theheat exchanger of Fig. 15;

Figs. 17 and 18 are plan views of different forms of foraminous platesand associated separators; and

Fig. 19 is a schematic view of a gas turbine system embodying a heatexchanger constructed in accordance with the present invention.

A heat exchanger constructed in accordance with the present inventioncomprises a plurality of substantially identical flat foraminous platesof relatively high thermal conductivity, and fenestrate or frame-likseparators alternating with the foraminous plates and formed withone ormore ligaments extending between opposite edge portions of theseparators. The plates may be of cast iron, steel, copper, aluminum orthe like suitable metallic material, although for certain usesnon-metallic compositions, such as a petro-- leum coke base carbonrendered impervious by impregnation with a synthetic resin (Karbate),may advantageously be used.

The separators may be of any suitable material, metallic or nonmetallic,which preferably is at least partially deformable and hence any of thewell-known fibrous or nonfibrou gasket materials may be used, includingsuch soft metals as lead and lead alloys, etc., the particular selectionof both the material for the separators and the foraminous platesdepending upon the temperatures to which these elements are to besubjected and the character of the fluids to be treated.

Should there be any hazard due to the use of combustible material, aswhen oxygen is one of the fluids, it may be necessary to use for theseparators an inert or noncombustible material, such as an asbestoscomposition, a polytetrafiuoro-ethylene (Teflon) resin, a siliconeresin, or a glass fiber or mineral wool base impregnated with anoncombustible binder such as a silicone resin, all of which materialsare particularly suitable since they are relatively deformable.

Although separators having some degree of deformability are preferred inorder to insure a gastightseal about the fluid passages, it is to beunderstood that, if desired, separators of relatively hard ornondeformable material, such as steel, etc., may be used in conjunctionwith foraininous plates of a relatively deformable material such asaluminum. In any event, as long as one of these elements is relativelysoft or compressible, as compared with the other, there will besufficient deformation of one of the contacting surfaces to insure agas-tight seal.

An alternative arrangement is to make each plate integral with one ofits adjacent separators. This may be done, for example, by forging aplate which on one side has integral ridges corresponding inconfiguration to those of the individual fenestrate separator hereindescribed. A sulficient number of these plates are then laid together toform a heat exchanger of the desired capacity. In such an arrangement itis necessary that the material of the plates and their integralseparators be sufficiently deformable o that a tight seal is attainablewhen they are clamped together; otherwise very accurate machining(which, though possible, is rarely practical) is required to insureabsolutely plane parallel surfaces and hence a tight seal.

As another modification of this construction, each plate may be madesimilarly but with an integral separator on each face, each suchseparator having for example one half of-the thickness of the individualfenestrate separator which would otherwise be used.

As still another modification, such plates may be made with integralseparators on each side, having the full thickness of the individualseparators, and these plates may then be laid up alternating with plainplates (i. e., plates without integral separators). If one component ismade of a sufficiently deformable material, and the other of asufllciently deformable or of a nondeformable material, as alreadydescribed in connection with the separate plates and separators, agas-tight seal is attained on clamping the structure together.

In any of these constructions employing integral separators, the facesof the separator ridges may be fiat, or they may be grooved or ridged orotherwise shaped and corresponding grooves or recesses are then providedin the opposite face of each plate into which the contours of theseparator ridges fit closely. While a degree of deformability is stillrequired in these integral plate-separator structures, the grooves,ridges or the like serve in particular to prevent any sideways slippageor movement of any of the plates.

The flatness of the plates, in any event, may be more or less relative,thus permitting plates having areas which are more or less cupped ordished, for increasing the surface contact area. In all cases, however,those portions of any one face of any plate which are in contact withthe corresponding separator (or plate, if the separators are integralwith the plate as above described) are fiat and in the same plane.Likewise, when punching or piercing the openings in the foraminousplates, it is possible to leave the metal which occupied the holes stillattached to the plate, in the form of tubular projections, orlouvre-like fins, or other shapes depending on the nature of thepunching operation. Such resulting configurations are permissible in theplates of the present invention in instances where such projections orfins do not occur in those areas of the plates which are in contact withthe separators to such an extent that proper sealing of the passages isprevented.

The plates and separators are so assembled that the openings in theplates are in substantial alignment and the ligaments of the separatorsare likewise aligned so as to surround or enclose the same number ofopenings in the plates, the ligaments thus defining a plurality ofregularly interrupted fluid passages, the size and shape.

tight seals about each of the passages.

If the openings in the plates are not in substantial alignment, thepressure drop through theapparatus isincreased and becomes excessive ifthe openings are greatly out of line. A slight degree of deviation fromperfect alignment will frequently occur; and slight deviation ispermissible as long as it does not have any significant effect upon thepressure drop through the heat exchanger. Expressed otherwise, thealignment should be such that substantially the lowest possible pressuredrop is attained with the particular configurations of plates used in agiven apparatus.

The opposite ends of the exchanger are provided with headers ormanifolds through which the fluids are admitted to and discharged fromthe heat exchange passages, and any suitable means may be provided forclamping or otherwise holding the parts in fixed position. Where thetemperature differential is substantial, spring-loaded tie rodsextending lengthwise of the fluid passages are recommended since theypermit both expansion and contraction without impairing the fluid-tightseals.

Since tie rods increase considerably the weight of the heat exchangerassembly, it may be advantageous in some instances to omit them, and tomake up instead a unitary structure of metal plates and separatorsbrazed together. This can be done, for example, by assembling togetherforaminous plates of copper, and separators of iron, and passing theassembly through a brazing furnace in an atmosphere of hydrogen, thereby.forming a bonded structure requiring no tie rods. use and the weight ofthe tie rods, but it is also free of any tendency toward sidewaysslippage of the plates and separators. On the other hand, it involves arelatively expensive brazing step, and the resulting structure cannot bepractically disassembled for cleaning or repair, so for most uses theherein described assembly using tie rods is preferred.

The openings in the foraminous plate may be of different size, shape andarrangement, depending upon the desired heat transfer coemcient andperformance characteristics (see Norris and Spofford, Transactions A. S.M. E. 64, 489). In most cases it is preferable to provide plates havingathickness less than the minimum dimensions of the openings therein andseparators having a thickness less than that of the contiguous plates,thereby providing interrupted fluid passages which induce a high heattransfer coeilicient between the fluid and the plate without causing anobjectionable resistance to flow. It is also im- Such a structure notonly eliminates the portant that the combined area of the openings inthe foraminous plate have a suitable relation to the area about theopenings, thereby to insure a good heat transfer from one section of theplate to and from all other sections consistent with the flowcharacteristics and thermal properties of the fluids. Thus, in the caseof gaseous fluids at reasonably low pressure (e. g., p. s. i. or less)the combined area of the openings may preferably be approximately equalto the area about the openings; whereas for most liquids the percentageof open' area may be considerably less than 50%; and for rarefied gasesthe optimum percentage of openings may be considerably greater than 50%.If desired, the percentage of open area in one fluid passage may differfrom that of another, depending upon the particular fluid to be handled.The optimum percentage of open area is also dependent upon the widths orcross-sectional shape of the fluid passages, because of the fact thatheat must be transferred from one passage to another, and the greaterthe length of the heat path the more metal is required to transmit heatin order to provide a proper delta T.

Where it is desired to provide a heat exchanger having fluid channels orpassages which may be varied, the foraminous plates are formed withregularly spaced openings and the separators are provided with ligamentshaving a width which is greater than the center-to-center distancebetween the openings and greater than the major dimension of theopenings. With this construction the ligaments may be so arranged as toinclose any desired number (within practical limits) of openings in theplates, thereby providing fluid passages of the desired size and shapewithout requiring specially designed plates.

The openings in the plates may, if desired, have more or less taperedsides, thus providing essentially a number of rows of little nozzles inseries throuhgout the length of the exchanger or any desired partthereof. When the plates are made by forging or die-casting, there isnecessarily at least a very small taper of the sides of the openings,and this taper can advantageously be appreciable when forging ordie-casting. The taper results in greater turbulence in they fluid flow,and hence in more effective heat transfer. On the other hand. itincreases the pressure drop. Hence the amount of taper, if tapering isemployed, should be such as will accomplish a proper and practicalbalance between heat transfer and pressure drop.

Another aspect of the invention relates to the separation of thecomponents of fluid mixtures, and more particularly to the separation ofoxygen from compressed air. In virtually all such systems it is thepractice to pass the incoming compressed air into heat-exchange relationwith the separated oxygen and/or nitrogen which are at relatively lowtemperatures. Where such heat exchange is conducted in a systemembodying a heat exchanger constructed in accordance with the presentinvention, there may be provided between two of the foraminous platesadjacent to the warm end of the exchanger, an injector for atomizing orotherwise injecting water into one or moreof the effluent passages,preferably the passages through which the nitrogen is flowing. Therelatively dry eilluent gas and heat absorbed from the incoming gas orair are effective to vaporize the injected water and due to the highlatent heat of vaporization of water, there is obtained a greatlyincreased cooling action which 15 enhances the over-all efficiency ofthe system.

A further advantage of a heat exchanger embodying a water injector isthat it provides a novel method for unbalancing a reversing heatexchanger such as is shown in the copending appiication of Samuel C.Collins, Serial No. 661,253, filed April 11, 1946, in which theunbalancing takes place at the cold end, through the conduction of thecooled compressed gas through a passageway in heat-exchange relationwith the cold end of the exchanger; whereas in a heat exchangerembodying the hereindescribed water injector, the unbalancing takesplace at the warm end of the exchanger in a very simple, efficient andinexpensive manner.

Moreover, in practically all systems for separating oxygen fromcompressed air, as well as other processes using compressed gases whichare conducted through a heat exchanger, the herein describedwater-injection arrangement may be advantageously employed as asubstitute for the expensive and cumbersome after-coolers which areconventionally used for cooling the compressed gases before they enterthe heat exchanger.

Another aspect of the invention relates to gas turbines and the likesystems wherein it is desired to transfer as much of the heat as ispractical from the exhaust combustion gases to the compressed air. Aheat exchanger constructed in accordance with the present invention mayadvantageously be used in all such installations due to the relativelylow pressure drop, high efficiency and low space requirements, ascompared to heat exchangers heretofore used.

A particularly advantageous feature of a heat exchanger constructed inaccordance with the present invention is that any given design may bereadily reproduced with substantially identical performancecharacteristics, thus permitting the replacement of one unit by anotherwithout the necessity of making compensating adjustments. The samestructural features likewise insure the provision of substantiallyidentical flow passages within the same heat exchanger so that it can beused in systems where the fluid flowis periodically reversed, such as isshown in the aforesaid copending application of Samue C. Collins.

Referring to the embodiment of Figs. 1 to 6, which shows what is nowconsidered to be one of the preferred forms of heat exchangers which maybe advantageously used in the above mentioned Collins system forseparating oxygen from air, the numeral I designates the heat exchangerwhich comprises a plurality of substantially identical foraminous plates2 interposed between separators 4 formed with ligaments 5. Since thisparticular application requires passages for the incoming air andoutgoing nitrogen and oxygen, the design of the plates and separators issuch as to provide nine separate fluid passages, as indicated in Fig. 2,the eight outer passages Al, A2, El, E2, etc., being for the air andnitrogen, and the inner passages C being for the oxygen.

Each of the plates 2 preferably consists of a die casting of copper,aluminum or other suitable material of good thermal conductivity, formedwith partitions or webs 6 corresponding to the ligaments 5 of theseparators, although as hereinafter shown, such plates may be of punchedsheet stock. The webs 6 cooperate with the lies.- ments 5 to define thenine fluid passages for the air, nitrogen and oxygen and, as aboveindicated, the separators are preferably of compressible, noncombustiblematerial such as a polytetrafluoro-ethylene (Teflon), a silicone resin,

asbestor, or a glass fibre or mineral wool base impregnated with asilicone resin. Between the webs 6, each plate is formed with aplurality of small, square-shaped openings 8 and a larger centralopening 10. As indicated in Figs. 3 to 6, the thickness of each platemay be of the order of two to three times that of the separators,thereby providing suflicient metal to insure a good heat transfer fromone section of each plate to another.

The plates and separators are assembled so that the ligaments arecoextensive with the outer faces of the webs 6 and thus not only insureproper spacing of the plates, but also gas-tight seals about each of thenine passages. When thus assembled, the openings 8 and III are insubstantially precise alignment and it will be noted, as illustrated inFig. 6, that the openings 8 define a plurality of regularly interruptedchannels in each fluid passage and that the channels are interconnectedso as to expose the maximum heat transfer surface of the plates. Afurther feature of this construction is that the channels defined by theopenings 8, being regularly interrupted, induce a high heat transfercoeflic.ent between the fluid and the plates without causing anobjectionable resistance to flow. Moreover, the fluid passages aresubstantially identical to each other and hence necessarily have thesame performance characteristics. Accordingly, the fluid flow throughthe different groups of passages may be reversed, as hereinafterexplained, without aifecting the balanced v operation of the system.

The plates and separators may, as above noted, be formed integral witheach other as illustrated in Figs. 5a to 5c and a sufficient number ofsuch plates are assembled to form a heat exchanger of the desiredcapacity. In Fig. 5a the plates 2 are formed on one face with integralseparators 4 and their ligaments 5 of full thickness, i. e., a thicknesssubstantially the same as that of the corresponding parts of theseparator 4 and, if desired, the upper faces of the separators 4including the ligaments 5 may be formed with ridges or projections I andthe corresponding parts of the undersurface of the plates may be formedwith grooves or recesses 9 to receive the projections I of thecontiguous separator, thereby providing an interlocking seal whichprevents lateral slippage of the assemblage. In all other materialparticulars each of the plates 2" may be substantially identical to theplate 2.

In Fig. 5b the plates 2 are formed on each face with integral separators4 and their ligaments 5' of half thickness, 1. e., a thickness aboutonehalf that of the corresponding parts of the separator 4. In Fig. 5cthe plate 2 is formed on each face with integral separators 4 and theirligaments 5 of full thickness and such plates alternate with the plates2 which may be of sheet metal or the like suitable material pierced toform tubular projections defining the opening 8", it being understoodthat, if desired, any other type of foraminous plate may be used inplace of the plate 2.

Although the openings in the plates herein described may be formed withlittle or no taper, as indicated in Figs. 4 and 6, if desired suchopenings may be of frustoconical shape or otherwise tapered, asindicated at 8 in Fig. 5c and at 8'' in Fig. 6a, in which case there isproduced a greater turbulence in the fluid fiow and hence a moreeffective heat transfer, although the pressure drop is increased asalready pointed out.

Thenumber and size or plates to be used in the heat exchanger willdepend on the desired capacity and having determined, empirically orotherwise, the heat exchange performance of a given number of plates andassociated separators, a heat exchanger of greater or lesser capacitymay be made by using more or less plates, as the case may be. Forexample, in the system illustrated in Fig. 1 the heat exchanger isdesigned to handle approximately 22 standard cubic feet of incoming airor gas per minute and approximately an equal amount of outgoing gaseswith a pressure drop through the exchanger of about 1.25 p. s. i. Theinlet and outlet temperatures of the gases at the warm end of theexchanger are about 80F. and 70 F., respectively, and the inlet andoutlet temperatures at the cold end are about 250 F. and --212 F.,respectively. Accordingly, the plates may be approximately 3 /2" square(over-all dimension) and about 0.12" thickness and a stack of 335 ofsuch "plates with interposed separators will provide a sumcient numberheat-exchanger elements to handle the above requirements.

Regardless of the number or type of plates employed, each of theopposite ends of the stack is provided with a header or manifold l2having partitions |4 corresponding to the ligaments and webs 6, and aclosure member It, as shown in Fig. ,2. The side walls of each headerare provided with openings is each communicating with one of the outerfluid pas ages, and each closure member is provided with a centralopening 20 communicating with the inner passage of the header, and eight1 small openings corresponding to and aligned with the openings ll! ofthe plates 2, which openings. as shown in Fig. 2, are centrally disposedwith respect to the passages defined by the ligaments 5.

The plates 2, headers 2, closure members it and interposed separators 4are flrmlv clamped together by eight tie rods 22 which extend throughthe stack from one header to the other. as illustrated in Fig. 2. Theopposite ends of the tie rods are threaded and carry clampin elementssuch as acorn nuts 24 and, if desired, short lengths of coiledcompression springs ,25 may be interposed between the nuts 24 at one endand the adjacent closure members to permit expansion and contraction ofthe stack without im airim. the seal ng action of the se arators.

In order 'toconnect the heat exchanger into the system shown in Fig. 1,the openings ll of the headers 2 at one end are connected with manifoldlines 30 and 3|, the line 30 and associated branches interconnecting thepassages A1 to A4 and the line 3| and associatedbranches inter onnectingthe passage'B1 to B4, and a single line 32 is connected to the opening20 of the adjacent closure member to provide a connec-- ing a casing 43having two chambers 4| and 42 separated by a medial partition. Thechamber 4| has an outlet 44 connected to the line 30 and another outlet45 connected to the line 3|. The chamber 42 has an outlet "connected tothe line 30 by a branch 41 and another outlet 43 connected to the line3| by a branch 49. Inlet lines 5| and 52 are respectively connected withthe chambers 4| and 42, the inlet line 5| being connected with asuitable source of compressed air and the line 52 either being connectedwith a receiver for nitrogen, or being vented to the atmosphere. Withinthe chambers 4| and 42 are piston valves 54 and 55 secured to a commonpiston rod 55, the outer end of which is connected to a bell crank 58pivotally mounted at 60. The bell crank 53 is periodically operated by amotor II, as explained in more detail in the aforementioned Collinsapplication, to shift the valves back and forth from one position toanother.

With this construction and arrangement compressed air admitted throughthe inlet line 5| passes through the chamber 4| and with the valves setas shown in Fig. 1 the compressed air passes from the chamber 4| throughoutlet 45 into the line 3| and its associated branches leading to thechannels B1 to B4 0! the exchanger. Simultaneously, gaseous nitrogenflowing in the opposite direction through the passages A1 to A4 isdischarged into the branches' 'associated with line 34, then into thebranch 41, chamber 42 and through the outlet 52. A

The o posite end of the exchanger 'may be connect d either to the sametype of va ve mechanism, or to the check valve arrangement herein shown,which is automatically operative to alter the. flow through the heatexchan er in accordance with the position of the valves 54 and 55. Thecheck valve arrangement com rises a line 65 connected at one end withthe outlet of a check valve 66 and at its other end to a T 61,

one branch 01' which is connected to the line 35 and the ot er branchwith the inlet of a check valve 63. The inlet of check valve 66 isconnected with a T,-10, one branch of which is connected with thenitrogen line 12 (leading from the processing'apparatus) and the otherbranch with the inlet end of a third check valve 14. The outlet of checkvalve '14 is connected with a T 15, one branch 01' which is connected tothe line 36 and the other branch to the inlet of a fourth check valve16, the outlet of which is connected to a line 13, The outlet of thecheck valve is connected to a T 80, one branch 0! which is connected tothe compressed air line 82 (leading to the processing apparatus) and theother branch is connected with the line 18.

With this arrangement and with the valve mechanism-set as shown in Fig.1., the compressed air admitted through inlet BI is conducted throughthe line 3| and associatedbranches into the passages B1 to B4, thenthrough the line 36 Thus, the lines 3| and 36 provide a communi- Ication with the passages B1 to B4, the lines 30- line 65, T 61 into line35, it being understoodthat the greater air pressure in. the lines 36and 18 is effective to hold the check valves 68 and 14 closed so thatthe flow of nitrogen is'confined to the line and 35. The line 35 andassociated branches conduct the nitrogen into the passages 11 A1 to A1from which it is discharged into the line 30 and associated branches,then through the branch 41, chamber 42 and outlet 52.

When the motor BI shifts the valves 54 and 55 to the opposite ends ofthe chambers 4| and 42 (in which position the valves close the ports 45and 43 and open the ports 44 and 43) the incoming compressed air passesthrough the line 30 and associated branches into the passages A1 to A1,and then into line 35 and associated branches. The line 35 conducts theair through T 61, check valve 60, 'r 80 into l ne 82. The pressure ofair in t e associated lines 65 and 18 is effective to hold the checkvalves 66 and I6 closed so that the flow of nitrogen thro gh the checkvalve 66 and line 65 is now arrested. The closing of check valves RR and6 is effective to force the nitrogen in the line 12 thro gh check valveI4 into the line 36 and its associated branches, and then through thepassages B1 to B4 of the heat exchanger. After passing through the heatexchan er the nitrogen is then conducted through line 3I and itsassociated branches into the branch 49 through port 40, chamber 42 andoutlet 52. This flow continues until the motor GI again shifts the vaves 54 and 55, thereby to cause the first operating cycle to berepeated, as explain d more fully in the aforementioned Collins aplication.

During the above described cycles the oxy en from the processingapparatus continues to flow into the line 31, passage C and the outletline 32, although in some in tanc s the oxygen may be collected beforepassing through the heat exchanger. in which event the center passage Cis not used, but s ch non-use does not interfere with the abovedescribed operation.

Use of the heat exchanger of the present invention ermits a lengthen ngof the cvcle of the process shown in the aforesaid Collins app ication.due to the fact that the condensing solids (such as CO2) tend to collectin the s aces between the plates rather than exclusively along the wa lsof the passages. Hence there is a less ra id clogging of the passageswith condensing solids t an wh n using the exchanger shown in the Collns ap lication.

The heat exchanger I00. shown in the embodiment of Figs. 7 to 14. isbasicallv the same as that of Figs. 1 to 6 and is designed for use in asystem simi ar to that shown in Fig. 1. with the exce tion that theoxygen assage is eliminat d.

In t is art c lar d si n there is provided sixteen fluid pa sages forthe incoming air and sixt en passages for the outgoing nitrogen, a totalof thirt -t o substantiallv identical passages arranged in fourtransversely extending groups.

T e heat exchanger I comprises a plurality oi flat, rectangularperforated plates IOI (Fig.

11) inter osed between separators I02 (Fig. 12) formed th tran verselyand lon itudinallv extending ligaments I03 and I04 which define thethirty-two fluid passages. Each of the plates IOI may be of cooper,aluminum or other suitable material as above noted, and the separatorsmay be of any suitable gasket material exhibiting some degree ofdeformability.

As shown more clearly in Fig. 13, each of the plates IIII is formed witha plurality of circular holes I05 disposed in transverse rows offsetwith respect to those in the adjacent rows, and the ligaments I04 have awidth exce ding both the diameter of the holes I05 and thecenter-to-cen'rer distance between the holes. Hence, when a plate IOI isinterposed between two separators I02, the

ligaments I03 and I04 seal 01! the underlying openings, as illustratedin Figs. 13 and 14, to provide the fluid passages A1 to A111 and B1 toB16, each of which comprises a plurality of regularly interrupted flowchannels, defined by the aligned openings I05 and having substantiallythe same flow characteristics as illustrated in Fig. 6. Since theseparators are of relatively compressible material, they may becompressed or deformed so as to interlock with the openings I05 of theplates, as indicated in Fig. 14, thus providing gas-tight seals betweenthe fluid passages. This interlocking also guards against sidewaysslippage or movement of the plates and separators, which is anotheradvantage which may be derived from the use of the present invention.

A stack of plates I0l with interposed separators I02 constitute the bodyof the heat exchanger and at each end of the stack there is provided aheader or manifold I I0 (Figs. '7 to 10). Each header consists of aunitary casting which may be of aluminum, cast iron or a like material.The inner body portion of each casting, as shown in Figs. 9 and 10, isformed with eight longitudinally extending channels corresponding to andaligned with the longitudinally disposed passages of the heat exchangerbody. These channels are designated (Figs. 9 and 10) A, B, etc., andcommunicate respectively with the passages designated A1 to A16 and B1to B16.

The outer body portion of each casting is formed with four compartmentsI I I, I I2, I I3 and I I4, as shown in Figs. '7 and 8, and the wall orweb H6 separating these compartments from the channels A, B, etc., isprovided with spaced openings I I8 (Figs. 8 and 10) arranged so that allthe A channels communicate with compartments III and I I3 and all the Bchannels communicate with compartments H2 and H4. Thus, the fluidpassages A1 to A16 are interconnected with each other with thecompartments III and H3; and likewise the fluid passages B1 to B18 areinterconnected and communicate with compartments H2 and H4. The fourcompartments are provided with closure plates I2I to I24 (Fig. 8) formedwith openings by which the compartments may be connected in pairs III,H3 and H2, H4 by conduits (not shown), thereby providing common inletand outlet lines for each group of passages.

The assembly of plates I0 I, separators I02 and headers H0 is firmlyclamped together by externally disposed spring-loaded tie-rods I26, theends of which are connected in any suitable manner with the outwardlyextending lateral flanges I20 formed integral with the headers IIO, asshown in Figs. 7 to 10.

Where, as here shown, the heat exchanger is designed for use in a systemsuch as illustrated in Fig. 1, the compartments III to H4 of the headersI I 0 may be connected with a valve mechanism and check valvearrangement in a manner corresponding to that shown for the heatexchanger I.

Referring to the embodiment of Figs. 15 to 18, the heat exchanger I40 isof the non-reversing type, but is designed to secure an additionalcooling effect by reason of a water injector. The exchanger l40comprises a plurality of foraminous plates which may be of the typeillustrated in Fig. 17 or Fig. 18, depending upon the contemplated useof the heat exchanger, but in either case the plates are interposedbetween fenestrate separators I42 formed with ligaments I44 which definethree elongate fluid passages A, B and C, the outer passages A and Cbeing for the outgol3- ing gas or fluid, e. g.,' the nitrogen in thesystem illustrated in Fig. 1, and the central passage B being for theincoming gas, e. g., the compressed air of the aforesaid system.

- The plates I ll (Fig. 17) are formed with a longitudinally alignedouter group of rectangular openings I45 and aninner group oflongitudinally aligned rectangular openings I46 separated fromeach'other by longitudinal webs I48 corresponding to the ligaments I,the size and shape of the openings I45 and I46 being designed to insurethe most eflicient heat transfer consistent with the flowcharacteristics and thermal properties of the fluids to be treated. Theplates Idla (Fig. 18) are substantially the same as those of theembodiment shown in Figs. 7 to 14 and the openings a therein and thecenter-to-center distance between these openings are smaller than thewidth of the ligaments I 44 of the separators so as to permit the fluidpassages to be sealed in a manner previously described. It will be notedthat with either type plate the fluid passages A, B and C each consistsof'a plurality of regularly interrupted flow channels havingsubstantially the same flow characteristics as illustrated in Fig. 6.

A stack of plates and interposed separators constitute thebody of theheat exchanger and at a point spaced from its warm end, i. e., a pointwhere the temperature of the outgoing gas is above 32 F., there isinterposed a water injector I50 (Fig. 16) which comprises a rectangularframe-like member having two longitudinally extending spaced arms I 52and I53, the shape of the upper and lower surfaces of the injectorcorresponding to that of the separators so as to insure a gas-tight sealwhen assembled as shown in Fig. 15L The arms I52 and I53 are providedwith longitudinally extending ducts I54 and I-55 which extend throughthe end wall I56 of the injector, as shown in Fig. 16. A plurality ofspaced minute openings I58 and I59 (here shown on an ex: agg rat dscale) are formed in the outer side walls of the arms and extend at anangle in the direction of the flow of the fluid in the passages A and C.

With this construction and arrangement water admitted through supplylines I6I and I62 (Fig. 15) is discharged through the openings I58 and 5I58 in the form of a fine spray into the passages A and C, and as thetemperature of the gas at this point is above 32 F. and as the gas isrelatively dry, the water is quickly vaporized with a consequent coolingof the gas. Thus, an additional cooling effect is produced and as aresult the incoming gas in the passage B is cooled to a greater extentthan would otherwise be possible.

At each end of the stack there is a header or closure I65 formed withthree ofl'set openings respectively aligned with the fluid passages A, Band C and which receive pipe lines I88, I61 and I68, respectively. Thestack is held in assembled relation by interiorly disposed spring-loadedtie rods I which extend through the fluid passages A and C, passingthrough the openings in the plates which may, if necessary, be enlargedso as to accommodate the tie rods.

This particular design of heat exchanger is not only useful in a systemof the type illustrated in Fig; 1, but also in any system where it isdesired to efiect' a heat exchange between two fluids, at least one ofwhich is a gas to which heat is to be transferred.

In Fig. 19 we have shown a heat exchanger constructed in accordance withthe present invention' associated with a gas turbine system whichprovides particularly advantageous application. In this embodiment theheat exchanger I80 may be made from plates and associated separatorswhich may or may not be integral, but in either case the heat exchangermay have either two groups of passages. such as illustrated in theembodiment of Figs. 7 to 14, or a single passage interposed betweenconnected outer passages, as illustrated in the embodiment of Figs. 15to 18, but in any case the size and shape of the two passages or groupsof passages, as the case may be, and the openings in the foraminousplates are designed to secure the desired performance for the particularinstallation. Because this particular application does not usuallyrequire a periodic disassembly of the heat exchanger, the use of the tierods may, if desired, be eliminated, in which case the assembled partsmay be brazed together, as above explained. Since the heat exchangermust withstand temperatures of the order of 500 F. or more, individualseparators if used should be of asbestos or the like noncombustible,infusible material, but in any case the foraminous plates, withorwithout integral separators, may be of cast iron, steel, copper or othersuitable material.

The inlet I8I at the cold end of the exchanger is connected by a pipeline I82 to the discharge port of a pump or fan I84 driven by the gasturbine I85, and the outlet I86 of the warm end of the heat exchanger isconnected by pipe line I81 to the combustion chamber I88 of the turbineI85. The exhaustport on the turbine is connected by a pipe line I90 tothe inlet I9I at the warm end of the exchanger and the outlet I92 at thecold end of the exchanger may exhaust to the atmosphere.

A particularly advantageous feature of this system is that the heatexchanger not only is effective to transfer the practical maximumavailable heat from the exhaust combustion gases to the incoming air,but furthermore the transfer is accomplished without an objectionablepressure drop in either passage, and the space requirements areparticularly low. Hence, a greater over-all efliciency of the system isattained than is possible with heat exchangers of conventional design. i

In addition to the advantageous features above noted, it will beobserved that a heat exchanger constructed in accordance with thepreferred form of the present invention may readily be disassembled forcleaning and repair and easily assembled without the necessity .ofbrazing, welding or soldering the parts. Since both the foraminousplates and separators forany given design are ordinarily identical, theymay be economically manufactured and assembled by mass productionmethods with the assurance that each, such unit will have substantiallyidentical performance characteristics, thereby permitting thesubstitution or replacement of one unit by another in any system withoutthe necessity of making compensating adjustments.

While we have shown and described difierent' inated structure with thecorresponding openings in said plates being uniformly disposed toprovide predetermined flow characteristics, said separators includingligaments surrounding a plurality of said openings to define a pluralityof regularly interrupted fluid passages, headers at the opposite ends ofsaid structure communicating with the passages defined by saidligaments, and means holding said structure and headers in assembledrelation.

2. A heat exchanger as set forth in claim 1, wherein the combined areaof the openings in each of said plates is approximately equal to thearea of the metal about said openings.

3. A heat exchanger as set forth in claim 1, wherein the thickness ofeach separator is less than that of the associated plate.

4. A heat exchanger as set forth in claim 1, wherein the openings insaid plates are of generally frusto-conical shape.

5. A heat exchanger as set forth in claim 1, wherein the holding meanscomprises spring loaded tie rods extending between said headers forclamping the assemblage together.

6. A heat exchanger as set forth in claim 1, wherein said plates areformed with uniformly spaced openings and said separators are of adeformable material having passage defining ligaments of a width greaterthan the center to center distance between adjacent openings in saidplates, the material of said separators being compressed so as toproject into the contiguous openings of the adjacent plates, thereby toprovide an interlocking seal.

7. A heat exchanger as set forth in claim 1, whereimthe foraminousplates are formed with uniformly spaced openings and said separators areof a deformable material having passage defining ligaments of a widthgreater than the major dimension of said openings, the material of saidseparators being compressed so as to project into contiguous openings ofthe adjacent plates, thereby to provide an interlocking seal.

8. A heat exchanger as set forth in claim 1, wherein said separators areintegral with said plates.

9. A heat exchanger as set forth in claim 1,

wherein said separators are integral with said plates and theircontiguous portions are formed with complementary interengaging groovesand projections constituting an interlocking seal effective to preventlateral slippage of the assembled plates.

10. A heat exchanger as set forth in claim 1, wherein said correspondingopenings are of substantially the same size and in substantialalignment.

11. A heat exchanger as set forth in claim 1, wherein an injector isinterposed between two of said foraminous plates at a point spaced fromone end of the heat exchanger, said injector having the same generalcross-sectional shape as said separators and being formed with armscorresponding to the ligaments of said separators, one of said armshaving a duct communicating with one of said fluid passages fordischarging a fluid therein.

12. A heat exchanger as set forth in claim 1, wherein an injector isinterposed between two of said foraminous plates at a point spaced from.

one end of the heat exchanger, said injector having the same generalcross-sectional shape assaid separators and being formed with armscorresponding to the ligaments of said separators, said arms havingducts communicating through a plurality of fine openings with at leastone of said fluid passages for admitting thereto a liquid in the form ofa spray.

HOWARD O. McMAHON. GUSTAVE A. BLEYLE, JR. RICHARD B. HINCKLEY.

REFERENCES CITED The following references are of record file of thispatent:

UNITED STATES PATENTS in the

